Let me preface by saying that I know that idle issues are very common on these injection systems and I have probably read all threads about this topic on here as well as other forums. I now have a good general understanding of the system and which components are involved. However my diagnosis so far was not successful in finding the culprit.
Let me also say that I know that the Idle Control Valve or the Idle Control Module are often the cause of these problems. I would love to simply replace both, but they are either very expensive or in the case of the Module simply not available new or rebuilt where I live.
The Problem: Intermittent surging idle + constant high idle (I have no tach, but sounds like around 1500 rpm). Both only happen once the engine is fully warmed up. Runs fine otherwise.
What I have done/checked so far:
- Checked, cleaned and readjusted fuse no. 6
- Thoroughly cleaned and lubricated the ICV (seems to by very snappy when manually applying 12V, buzzing when ignition is switched on)
- Swapped the Idle Control Module against a supposedly working used unit (not ideal I know but I don't have access to a new or refurbished one)
- Checked the 45° temp switch (this one was faulty. Since it is NLA I build a replacement myself which tests fine. After the replacement the surging was gone for a while, but has now returned but the switch still tests fine...)
- Checked the 0° temp switch (did not check if it will close below 0°, but above its open)
- Blue Coolant Temp Sensor (Mine was white and seemed fine but changed just in case since it is cheap and I had one fail on another car before)
- Checked brown Coolant Time Switch (Resistance seems to be in spec, not sure if this has potential influence on idle or not)
- All vacuum lines including J boot are new (I will smoke test again just to make sure but I think there is no vacuum leak)
- TPS "clicks" right on closing or opening the throttle
- Checked all connections to the Idle Control Module for continuity (*)
Pin 12 should have 12V when the car is in neutral? Where does this come from? Is there a switch somewhere?
The Idle Control Module still seems to be the most likely culprit at this point. How ever since I cannot buy one or would have to order a refurbished one from the US most likely which is very expensive, I want to be sure it is the cause of the problem. You read about these modules failing a lot but nowhere I could find what is actually failing inside of them. Today I opened mine up to look inside. My PCD diagnosing skills are limited and I cannot spot anything obviously wrong with it. I have access to a high quality multimeter and other tools if anyone can instruct me on what to test I might be able to do it.
Any further ideas are greatly appreciated.